Eastern Hog-nosed Snake (Heterodon platirhinos) COSEWIC assessment and update status report: chapter 2

• Previous page
• Table of contents
• Next page

COSEWIC Executive summary

Species information

The Eastern Hog-nosed Snake, Heterodon platirhinos Latreille 1801, is a medium-sized, stout-bodied, oviparous colubrid. Its apt common name is derived from the upturned scale, unique to hog-nosed snakes, at the tip of its snout. Individuals of this species are highly variable in colour and pattern, with phenotypes ranging from colourful and blotched to melanistic. However, its tendency, when approached by humans, to inflate its neck to a cobra-like hood, hiss, and strike, eventually defecate, roll onto its back with mouth open and tongue extended, and sometimes even exude blood from its mouth and/or cloaca is usually sufficient for its identification. Although this species is harmless, it is often killed by humans perhaps alarmed by its complex defensive behaviour. Slight sexual dimorphism occurs in this species, with males generally smaller than females.

Distribution

The Eastern Hog-nosed Snake occurs in both Canada and the United States, but less than 10% of its global range is in Canada. In Canada, the Eastern Hog-nosed Snake is restricted to southern and south-central Ontario and is found in two geographically distinct areas: the Carolinian Region of southwestern Ontario and the Great Lakes/St. Lawrence Region of central Ontario south of the French River and Lake Nipissing and east of Georgian Bay. This snake is extirpated from the Regional Municipalities of Halton, Peel and York, as well as Pelee Island, Point Pelee National Park and other more local areas. Also, the records from Bruce, Grey, and Prince Edward Counties are considered historic and H. platirhinos may be extirpated from these areas.

In the United States, the Eastern Hog-nosed Snake is present in all eastern states from southern New England, west to Minnesota and South Dakota, south to Texas and east to Florida.

Habitat

Six features have been used to define the preferred habitat of H. platirhinos: well-drained soil; loose or sandy soil; open vegetative cover such as open woods; brushland or forest edge; proximity to water; and climatic conditions typical of the eastern deciduous forest. Eastern Hog-nosed Snakes in shoreline areas often rely on driftwood and other ground cover in beach and beach dune habitats, where their prey of choice, toads (Bufo spp.), is found. South of Parry Sound, in the Georgian Bay region, Eastern Hog-nosed Snakes prefer open grass, sand, human-impacted and forest habitats over rock, wetland, and aquatic habitats. Because the Eastern Hog-nosed Snake is a prey specialist on toads, it is also important to consider habitat requirements and population trends of toads.

Habitats preferred by Eastern Hog-nosed Snakes have declined or disappeared because, coincidentally, these habitats have soils favourable for agriculture and beach/water-related recreation.

Biology

Eastern Hog-nosed Snakes appear to hunt mainly by olfaction. Snakes in the U.S. feed on toads, frogs and lizards, but they also feed on some insects, other amphibians, molluscs, birds, crustaceans, turtles, earthworms, and spiders. However, adult snakes in Canada appear to feed almost exclusively on toads (Bufo americanus and B. fowleri).

In Kansas, age at maturity is reached in approximately 2 years; however, in Canada, age at maturity may be delayed to 4-5 years. Captive individuals have lived 11 years. Copulation occurs in spring, and in August and early September; females may copulate with more than one male. The Eastern Hog-nosed Snake is oviparous; females lay between 7 and 37 eggs in nests in sandy soil about 10-20 cm below the surface, but also nest in cavities under rocks as well as under driftwood on beaches. Oviposition begins in late June and continues for 2-3 weeks. In Canada, in the northern portion of the species’ range, females may need to excavate nests in locations that provide enough sunlight to ensure appropriate thermal conditions for egg incubation.

Eastern Hog-nosed Snakes hibernate from October to April, do not exhibit communal hibernation, may or may not excavate their hibernation site depending on the availability of an acceptable pre-existing burrow, and may or may not exhibit hibernation site fidelity. The availability of hibernation sites may or may not be a limiting factor, depending on the area.

Eastern Hog-nosed Snakes may experience higher natural mortality by predation than other species of snake found in Ontario because they are active predators and are naturally a highly vagile snake. Predators include mustelids, foxes, other medium-sized mammals, owls and other raptors. Pet and feral cats and dogs are also likely predators. Eastern Hog-nosed Snakes in or near urban areas suffer high rates of added mortality from anthropogenic sources.

Population sizes and trends

It is difficult to estimate the abundance of Eastern Hog-nosed Snakes in Ontario because there are few studies incorporating data on population trends and abundance. However, Eastern Hog-nosed Snakes are found in low densities wherever density has been measured, with values from Canadian studies ranging between 0.04-0.004 snakes per hectare. The NHIC has ranked 8% of known element occurrences of Eastern Hog-nosed Snakes in Ontario as extirpated and another 35% of element occurrences as historic, or unconfirmed in the last 20 years. Based on these densities, the NHIC ranks of Element Occurrences and size of activity ranges, a crude estimate of total number of adults in Canada is less than 10,000. Ultimately, the decline in available habitat, the increase in road construction in south-central Ontario, and the threat of human persecution will result in a continuing decline in number of snakes. The Eastern Hog-nosed Snake is highly mobile, for a snake, which increases its susceptibility to urbanization and habitat fragmentation.

Although H. platirhinos is found in the U.S. directly south and west of Ontario, rescue effect from American populations of snakes would be virtually impossible. Canadian populations are separated from the American populations by the Great Lakes and H. platirhinos is currently designated as Vulnerable in Michigan, Ohio, and Pennsylvania.

Limiting factors and threats

Limiting factors for this species include the availability of suitable habitat, especially the sandy soils necessary for oviposition and hibernacula, and the availability of prey. Because these snakes are specialists on toads, declines and fluctuations in toad populations may cause declines in Eastern Hog-nosed Snake populations. However, Heterodon platirhinos has disappeared from Point Pelee and Pelee Island where Fowler’s Toads have also been extirpated, although American Toads remain common. The key threat to this snake is the ongoing proliferation of road networks which increase mortality and habitat fragmentation. Persecution by humans and collection for the pet trade also negatively affect this species’ survival.

Special significance of the species

The amazingly intricate defensive behaviour of H. platirhinos makes it, perhaps, the most interesting snake in Canada. The occurrence of this behaviour by H. platirhinosalso provides the opportunity to study the adaptive significance of death-feigning.

Existing protection or other status designations

The Eastern Hog-nosed Snake received status under COSEWIC in 1997 when it was designated as Vulnerable, and was reassessed as Threatened in 2001. It was designated as Threatened by the Ontario Ministry of Natural Resources in 2001. Also, this species is a “Specially Protected Reptile” under the Ontario Fish and Wildlife Conservation Act.

Heterodon platirhinos is listed at some level of peril in 11 of the 34 states where it is found. The Global status is G5; in the U.S., the national status is N5 and in Canada the national status is N3.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2007)

Wildlife Species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)^Footnotea

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)^Footnoteb

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)^Footnotec

A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.